Technical Abstract:
Ractopamine's effect on expression of proteins representative of cell proliferation (proliferating cell nuclear antigen, PCNA), cytoskeleton (desmin), and differentiation (myosin) were evaluated in mouse muscle C2C12 cells using microtiter immunocytochemical enzyme-linked immunosorbent assay. Cells were grown under culture conditions previously established for myoblasts and myotube differentiation. Antigen expression was evaluated relative to protein absorbance per well. Ractopamine (RAC) incubations (10uM, 48h) started on day 1 in culture (myoblasts), day 5 (differentiation period) or day 7 (established myotubes). PCNA was highest during the differentiation period. RAC increased PCNA in myoblast and myotubes ~20%. PCNA results in myotubes suggest RAC favors reinitiation of cell division in differentiated cultures. In comparison to myoblasts, desmin expression decreased ~25% in differentiated cells. RAC increased desmin expression ~10% over controls (day 7 and 9 harvest). As expected, no myosin expression was found in myoblasts, and myosin increased ~20% from day 7 to 9. RAC increased myosin slightly on day 7, but decreased it on day 9 (10%). Day 9 myosin results with RAC are consistent with concommitantly increased PCNA. RAC appears to have the capacity to increase proliferation of myoblast both before and after culture conditions favoring differentiation, as well as a capacity to increase myosin expression in myotubes. If these results are consistent in vivo, RAC's effect would be beneficial in the growing animal two ways: proliferation of satellite cells and increased myosin deposition in muscles.